This invention relates to improvements in fluid pressure servomotors or vacuum boosters for use in vehicle braking systems and, more particularly, to spring retaining devices for use in such servomotors.
The prior art is replete with various types of fluid pressure servomotors including a casing having a movable wall therein dividing the interior of the casing into two chambers, a valve body connected to the movable wall and receiving a valve mechanism therein for connecting one of the chambers selectively with the other chamber or with a source of fluid pressure such as the atmosphere, and an input rod mounted in the valve body to operate the valve mechanism. Usually, the input rod is normally urged by a spring in the direction separating it from the valve mechanism or in the direction projecting outwards of the valve body.
In connecting the spring with the input rod, a radial shoulder has usually been formed on the circumference of the input rod facing toward the inner end thereof to cooperate with a spring retainer abutted by the outer end of the spring. Such construction operates satisfactorily, but it has sometimes been required to exchange the spring or a valve member (usually formed of resilient material) of the valve mechanism or to extract the same outwards of the valve body with the input rod being located in its position. One prior art construction connecting the spring releasably with the input rod comprises an annular flange or an increased diameter portion formed on the input rod to define an inwardly facing shoulder, an annular spring retainer having an inner diameter larger than the outer diameter of the input rod, and a stop ring disposed between the retainer and the shoulder of the input rod. The spring retainer and the spring can easily be removed from the input rod over the outer end thereof. However since the inner diameter of the retainer is sufficiently larger than the corresponding outer diameter of the input rod, it has been difficult to maintain the retainer coaxially with the input rod thus preventing proper operation of the spring and causing undesirable wear of seal members.